in the webassist/kfm/initialize.php file, change the following line:
$kfm->defaultSetting('banned_extensions',array('asp','cfm','cgi','php','php3','php4','php5','phtm','pl','sh','shtm','shtml'));
to:
$kfm->defaultSetting('banned_extensions',array('asp','cfm','cgi','pl','sh','shtm','shtml'));